The present invention relates to an optosemiconductor device and the method for its manufacture, and especially to a method for producing an optosemiconductor device, which is greatly improved in its light emission efficiency and heat-radiation capability.
Generally, optosemiconductor devices are such parts as perform transmission of light via electric signals, and are largely classified into ordinary light-emitting diodes, which convert electric signals into optical signals and use them in forward output and light-receiving diodes (phototransistors, photodiodes, triac, photo IC), which receive optical signals and convert them into electric signals. These optosemiconductor devices are manufactured in products of a wide wavelength range, from visual to infrared lights, according to the different kinds, density, and structure of the impurities forming the PN junction of semiconductor crystals.
Below, the optosemiconductor devices are described, taking the light-emitting diode as example.
The light-emitting diode is a light-emitting element so called an injection-type electro-luminescence of the p-n junction, and it can operate with very low voltage and has a long life span, wherefore, it is in very wide use as solid indicating element or as indicator of pictorial images, etc.
The structure of the light-emitting diode is given in FIG. 1. It consists of a chip 2 which emits light when power is applied to a cathode lead 3 and anode lead 4, both the latter made of a conductive metallic material for application of electricity to the said chip 2; the said chip 2 being attached to a pad 5 of the shape of a cup formed on an end of the said cathode lead 3 by conductive adhesive, and at the same time is bonded with the end of the said anode lead 4 by a wire 6, that is, electrically connected between the said cathode lead and anode lead 3, 4.
As is seen in FIG. 2, the said chip 2 is molded by a mold 7 of an insulation material for its protection against influence from outside, but it is so structured that parts of the other ends of both the cathode lead and anode lead 3, 4 are exposed to outside so that power can be delivered to the said chip 2 from outside.
When the said exposed parts of both the cathode lead and anode lead 3, 4 of the light-emitting diode 1 are connected electrically with a circuit and power is delivered to the said chip 2 through the said cathode lead and anode lead 3, 4, the light-emitting diode begins to emit light. the mold 7 is generally composed of epoxy resin and is made, according to the wavelength of the light-emitting diode 1, in red, green, orange, and other colors, or colorless transparency.
However, in the existing diodes like this, the emission of light of the light-emitting elements invariably gets lower under the mounting thermal stresses inside the package, while their light-receiving elements are apt to suffer deterioration of their light-receiving efficiency by decrease in the amount of light they convert to electric signals, if they are subject to prolonged use.
In the case of ideal light-emitting diode, the emission of light is in proportion to the forward current. This is limited to the case of an ideal light-emitting element which does not generate heat. Otherwise, as the forward current increases, the temperature of the light-emitting diode rises causing the light emission efficiency to decline. In short, the rise of temperature in the light-emitting member does not merely degrade the light-emission efficiency but destroys the junction of the p-n joining of the light-emitting chip, thus causing decrease of its duration.
In other words, if the heat generated in the light-emitting (or light-receiving) chip is not efficiently discharged out of the package the light-emission efficiency (the light-reception efficiency in the case of the light-receiving element) of the chip degrades and its reliability cannot be secured.
The present invention is intended to overcome these problems by providing an opto-semiconductor device excellent in heat-radiation and of high reliability along with a method for its manufacture.
Another objective of the present invention is to provide an optosemiconductor device of a desired wavelength range by combining fillers of various hues and a method for its manufacture.
Yet another objective of the present invention is to provide an optosemiconductor device which has an improved efficiency in light emission by radiating the light in the forward direction without loss, along with a method for its manufacture.